The default SSH password for root is libreelec and cannot be changed. If you need to access the host using SSH and you want to secure it, just disable SSH passwords and use certificates.
Copy your public RSA key to the LibreELEC device and change the SSH configuration. The SSH daemon configuration is /storage/.cache/services/sshd.conf, set it to:
SSHD_DISABLE_PW_AUTH="true" SSH_ARGS="-o 'PasswordAuthentication no'"
Restart the daemon with systemctl restart sshd.service.
The daemon is running, edit your crontab with crontab -e.